1. Field
This disclosure is generally concerned with therapeutic antibody or immunoglobulin preparations and specifically with therapeutic immunoglobulin preparations that include at least some antibodies of the IgM type.
2. Prior Art
Antibodies may be classified according to a well known typing system (i.e. IgM, IgG, IgA, IgD, IgE) and, in case of IgG, according to sub-types (i.e. IgG.sub.1, IgG.sub.2, IgG.sub.3, and IgG.sub.4).
Commercially available immunoglobulin preparations (known as immune serum globulin or ISG) commonly consist mainly of antibodies of the IgG type with the distribution of IgG sub-types approximating that found in human plasma. Typically, the amount of IgM in such preparations, if present at all, is relatively small.
IgM is a well known 19S immunoglobulin which comprises about 7% of the immunoglobulins-found in man. IgM antibodies are said to have an antibody valence of at least five and they are the earliest antibodies generated in an immune response. Although IgM antibodies tend to be very effective, especially in combating bacterial infections, they have a relatively short in vivo half life of about five days. Further, IgM antibodies tend to aggregate and are relatively difficult to stabilize, especially in purified form.
To date, the only known commercial intravenous (IV) product having significant amounts of IgM antibody is a product known as Pentaglobin.TM., available from Biotest, GmbH, of West Germany. The use of that product appears to be described in articles by K. D. Tympner, et al, "Intravenous IgM-Applikation", Mschr Kinderheilk 123,400-401 (1975) and by K. N. Haque, et al "IgM-Enriched Intravenous Immunoglobulin Therapy in Neonatal Sepsis" Am. J. Dis. Child. 142, 1293-1296 (1988). That product comprises, on a percent by weight total protein basis, about 76% IgG, about 12 % IgA and about 12 % IgM.
It has been thought that the use of larger amounts of IgM in an ISG product could lead to adverse reactions. For example, it is known that IgM is many times more potent than IgG in activating the complement cascade in an immune reaction. This is because only one molecule of IgM bound to an antigen will activate complement whereas two or more molecules of IgG must be bound to an antigen in close association to each other to activate complement.
It appears that the very production methods used in preparing IgM-enriched products may limit the amount of IgM available due to degradation reactions. See, for example, U.S. Pat. No. 4,318,902 to W. Stephen, describing the use of .beta.-propriolactone to make an IgM enriched product IV administrable. Hence, for whatever reason, even though IgM is recognized as very effective, it has not appeared in any commercially available intravenously useful ISG product at an amount greater than about 12% by weight total protein. Although a 20% by weight IgM product has been available, in the past (Gamma-M-Konzentrat, Behringwerke AG, Marburg, Germany), it has been made for and limited to intramuscular (not IV) applications.
Various purification schemes have been suggested for plasma-derived IgM and, more recently, monoclonal-derived IgM. In the case of plasma-derived IgM, it has been known since the 1940's that alcohol fractionation techniques could be used to obtain a relatively concentrated IgM from what is known as Cohn Fraction III. See also, for example, the above-cited U.S. Pat. No. 4,318,902 (and the cited references) to W. Stephen concerned with the use of beta-propriolactone to make a concentrated (12%) IgM suitable for intravenous (IV) administration. In addition, see EPO application 0 038 667 of Miura et al (IgM acylation). Other IgM purification or preparation techniques are disclosed by U. Sugg et al, Vox Sang. 36:25-28 (1979); M. Steinbach et al, Preparative Biochemistry 3 (4), 363-373 (1973) and A. Wichman et al, Biochem. Biophys. Acta 490:363-69 (1977). For a variety of technical reasons, plasma derived IgM has been relatively difficult to purify and the highest known purity to date (used in analytical purposes) is about 90% IgM, by weight.
In addition to the above problem associated with IgM-rich preparations, it has been observed that the preparations in use tend to generate what is known as non-specific complement activation. Non-specific complement activation refers to the initiation of the complement cascade even in the absence of antibody-antigen complexing. This phenomenon is often associated with the infusion of aggregates of immunoglobulins. Non-specific complement activation is to be avoided since it may cause undesirable side effects such as hypotension. Specific complement activation, on the other hand, is desirable and it occurs only after the immunoglobulin(s) has bound to, for example, the antigenic surface of a microorganism in the bloodstream.
It has been reported by S. Barandun et al "Intravenous Administration of Human Gamma-Globulin", Vox Sang 7, 157-174 (1962) that human gamma-globulin for intravenous administration heated at 37.degree. C. at pH 3.8-4.0 for 24 hours, followed by pH adjustment to 7.0, resulted in a reduction of anticomplementary activity (AC) measured by complement fixation test. However, this treatment for longer periods of incubation resulted in high anticomplementary activity due to the formation of aggregated gamma-globulin. These authors did not demonstrate retention of specific complement activity by the heated immunoglobulin when bound to antigen. Furthermore, no demonstration of in vivo safety was reported by these authors. In addition, M. Wickerhauser et al "Large Scale Preparation of Macroglobulin", Vox Sang 23, 119-125 (1972) demonstrated that IgM concentrates prepared by PEG precipitation had high anticomplementary activity (AC) by standard complement fixation test and this AC activity was reduced 10 fold by incubating the IgM concentrate at pH 4.0 at 37.degree. C. for 8 hours followed by readjustment to neutral pH. Similar to the previous paper (Vox sang 7, 157-174 (1962), these authors did not assess the specific complement activating potential of the heated IgM concentrate, nor did they assess safety in any animal model.
We have now found that the problem of non-specific complement activation associated with IgM or IgM rich immunoglobulin preparations can be minimized (without losing specific complement activation) in a relatively simple and surprising way.